Interpretive Summary: Contamination of apple cider and apple juice by human pathogens such as E. coli O157:H7 has been reported in recent years. Thermal processing is the most commonly used technique to reduce spoilage and pathogenic microorganisms as well as to inactivate enzymes in juice. Unfortunately, thermal pasteurization can produce undesirable quality changes like loss of color and flavor. Recently, non-thermal processing alternatives like pulse electric field (PEF) and ultraviolet (UV) treatment have been examined for their efficacy in extending shelf life and enhancing microbial safety while minimizing quality and nutritional losses. However, little information exists on the effects of these processes on flavor of apple cider. This study was conducted to investigate the aroma composition of apple cider treated by PEF, UV, or thermal pasteurization during 4 weeks storage at 4 C. Results showed that stored UV processed apple cider possessed a fermented, rotten aroma due to microbial spoilage and differed significantly from untreated fresh apple cider. No difference was detected by panelists between PEF treated and untreated fresh apple cider. The odor of PEF processed cider was preferred by 91% panelist over that of thermally processed cider and was described as having stronger apple aroma. This coincided with instrumental analyses which found the concentrations of ester and carbonyl volatiles in PEF processed cider increased during storage. The information will help juice processors to adopt PEF technology for the enhancement of apple cider safety and quality.

Technical Abstract:
Aroma composition and microbial quality of identical lots of apple cider treated by pulsed electric field (PEF), ultraviolet irradiation (UV), or thermal pasteurization and stored at 4 C were compared at 0, 2 and 4 weeks. Conditions for all three treatments were adjusted to produce identical 5 log reductions in microorganism levels. PEF and thermal pasteurization maintained acceptable microbial quality for 4 weeks but UV samples only lasted 2 weeks. No significant aroma volatile differences were observed between sample treatments immediately after processing. However, after 4 weeks storage, thermal and UV processed samples lost 30% and 70% of initial total ester and carbonyl aroma volatiles respectively whereas a 20% increase was observed for PEF processed apple cider. There were 25 aroma active volatiles in the unpasteurized cider, compared to 23 in the PEF samples and 21 and 16 in thermal and UV samples respectively. Triangle sensory analysis indicated that the aroma of thermal and UV treated cider stored for 4 weeks differed significantly (p<0.05) from fresh untreated cider The aroma of PEF treated apple cider was preferred by 91% of the 50 person consumer panel compared to that of thermally processed cider.